Mayonnaise spreads, known for about 200 years, commonly are formulated with a high content of fat or oil, and a correspondingly low content of moisture. Ingredients commonly used to constitute mayonnaise include edible vegetable oil, vinegar, lemon juice and/or lime juice, egg yolk and any of various flavorings, seasonings or spices. In view of these ingredients, it is seen that mayonnaise spreads typically are acidic; the aqueous component of the spread accordingly contains the acid and has a low pH. Mayonnaise spreads such as these are subject to spoilage; nevertheless, because of the low water content and the acidic pH, the extent and nature of contamination tend to be moderate. In particular, any contaminating microorganism must be able to tolerate the low pH and acid content of the mayonnaise spread. For this reason, common contaminants include certain members of the genus Lactobacillus, various members of the genus Bacillus, as well as certain yeasts, such as various members of the genus Saccharomyces (Smittle, J. Food Protection 40:415-422 (1977)). Lactobacilli are classified as homofermentative and heterofermentative. Lactobacilli that produce only acid when grown on any substrate are homofermentative. Heterofermentative lactobacilli produce both acid and a gas. These contaminants, upon proliferation, may lead to spoilage of the mayonnaise, and consequently to the loss of the spread and any food to which it has been added.
An interest of the public in recent years has been directed to consumption of foods containing lower quantities of fats and oils. This has led to the development of mayonnaise spreads with lower contents of these components. Whereas in conventional mayonnaise spreads the fat content may be about 50% or greater, low fat containing mayonnaise spreads may contain about 30% fat, or less, and spreads that are considered to be essentially fat-free may contain about 3% fat or less. The volume content lost when the fat is eliminated is generally compensated by including higher contents of the aqueous phase. In order to maintain the consistency associated with a mayonnaise spread, the aqueous phase is usually supplemented with a component to preserve the viscous, spoonable character of the spread, such as starch or a similar polysaccharide.
The increased content of moisture in low-fat and fat-free mayonnaises has certain consequences that must be addressed, however. First, a higher content of water renders the mayonnaise spread more susceptible to microbiological growth. Second, preserving the acid content of the aqueous phase similar to that present in conventional mayonnaise compositions, especially the incorporation of vinegar and citrus juices, results in a spread with a tartness that the consuming public tends to find objectionable. Efforts to reduce the tartness by diminishing the acid content, however, raises the pH and makes the low-fat spread more susceptible to microbiological contamination.
In one approach to this problem, food products containing acids, including mayonnaises and salad dressings, are formulated with fumaric acid, or with fumaric acid in combination with a food acidulent (U.S. Pat. No. 4,756,919). It is stated that microbiological spoilage attributable to lactic acid bacteria, in particular lactobacilli, is prevented with or without the use of chemical preservatives and/or the need for lengthy thermal processing times.
A similar approach to reducing tartness in salad dressings is disclosed as substituting acetic acid by any of various other organic acids, or phosphoric acid, in whole or in part (U.S. Pat. No. 4,927,657). According to this invention, tartness is reduced, in part, by providing buffers which increase the pH of the dressing product and confer enhanced mildness.
Alternatively, EP 0 689 773 discloses preserving the pH in mayonnaise spreads and dressing products as low as 3.5 or less, or preferably 3.3 or less, by using glucono-delta-lactone to retard microbial spoilage, alone or in combination with acetic acid. This formulation, it is disclosed, retains desirable organoleptic properties and minimal objectionable acidic bite. Additionally, antimycotics such as sodium sorbate, potassium sorbate, and benzoates are used as preservatives.
Nisin has also been used to help stabilize various food products. Nisin is a peptide-like antibacterial substance produced by microorganisms such as Lactococcus lactis subsp. lactis (formerly known as Streptococcus lactis). Its structure is illustrated in U.S. Pat. No. 5,527,505 to Yamauchi et al. The highest activity preparations of nisin contain about 40 million IU per gram. A commercial preparation, NISAPLIN.TM., containing about 1 million IU per gram is available from Aplin & Barrett Ltd., Trowbridge, England. Nisin has no known toxic effects in humans. It is widely used in a variety of prepared dairy foods. Experimental use in preserving other foods has also been reported. Details on these applications are provided below.
A number of efforts have been reported since 1975 directed to reducing uncoupled acid production in dairy fermentations by controlling the post-fermentation acidification of yogurt. In some of these studies, a nisin producing culture was introduced in an attempt to inhibit these effects. Kalra et al. (Indian Journal of Dairy Science 28: 71-72 (1975)) incorporated the nisin producing culture Streptococcus lactis (now known as L. lactis subsp. lactis) along with the yogurt culture before fermentation. Others introduced nisin in milk prior to fermentation (Bayoumi, Chem. mikrobiol. technol. lebensm. 13:65-69 (1991)) or following fermentation (Gupta et al., Cultured Dairy Products Journal 23: 17-18 (1988); Gupta et al., Cultured Dairy Products Journal 23: 9-10 (1989)). In all cases, the rate of post-fermentation acidification was only partially inhibited by these treatments and the yogurt continued to become more acidic throughout its shelf life.
In U.S. Pat. No. 5,527,505, by Yamauchi et al., yogurt was produced from raw milk by incorporating a nisin-producing strain, Lactococcus lactis subsp. lactis, along with the traditional yogurt culture consisting of Streptococcus salivarius subsp. thermophilus (ST) and Lactobacillus delbrueckii subsp. bulgaricus (LB). Yamauchi et al. teach that the lactococci are needed to secrete the nisin, whose effect is to retard the activity of ST and LB. The resulting yogurt therefore contains the lactococci used to produce the nisin. Nonetheless, the acidity of yogurt containing the nisin-producing bacteria increased by 64% to 96% in 14 days, in various experiments inoculated with differing amounts of L. lactis subsp. lactis, compared to the initial acidity at the completion of fermentation. Other studies (Hogarty et al., J. Food Protection 45:1208-1211 (1982); Sadovski et al., XX International Dairy Congress, Vol. E: 542-5-44 (1978)) also noted acid production and development of bitterness at low temperature by some mesophilic starter lactococci in dairy products.
Chung et al. (Appl. Envir. Microbiol. 55, 1329-1333 (1989)) report that nisin has an inhibitory effect on gram-positive bacteria, such as L. monocytogenes, Staphylococcus aureus and Streptococcus lactis, but has no such effect on gram-negative bacteria such as Serratia marcescens, Salmonella typhimurium and Pseudomonas aeruginosa when these microorganisms are attached to meat.
In U.S. Pat. No. 5,015,487 to Collison et al., the use of nisin, as a representative of the class of lanthionine bacteriocins, to control undesirable microorganisms in heat processed meats is disclosed. In tests involving dipping frankfurters in nisin solutions, the growth of L. monocytogenes was effectively inhibited upon storage at 4.degree. C.
Nisin has been added to cheeses to inhibit toxin production by Clostridium botulinum (U.S. Pat. No. 4,584,199 to Taylor). U.S. Pat. No. 4,597,972 to Taylor discloses a detailed example in which chicken frankfurter components are shown to require the presence of both added nitrite and added nisin in order to prevent or delay botulinum toxin production when challenged with C. botulinum.
Nisaplin.TM. has been found to preserve salad dressings from microbiological contamination, such as challenge by Lactobacillus brevis subsp. lindneri, for an extended shelf life period (Muriana et al., J. Food Protection 58:1109-1113 (1995)).
Maas et al. (Appl. Envir. Microbiol. 55, 2226-2229 (1989)) report that lactate, when incorporated into a turkey meat vacuum-packed composition, delays the generation of botulinum toxin in a manner directly dependent on the concentration of lactate introduced into the composition. Maas et al. do not mention nisin.
In U.S. Pat. Nos. 4,888,191 and 5,017,391, Anders et al. disclose compositions and methods related to the use of lactate salts to delay C. botulinum growth in a foodstuff such as fish or poultry. The foods are heated to a temperature sufficient to cook the meat but not to sterilize the product. Anders et al. suggest that lactate may be used alone, or in combination with other agents such as sodium nitrite. These patents fail to discuss nisin or its properties.
There remains a need to prepare low-fat mayonnaise spreads and essentially fat-free mayonnaise spreads that resist spoilage brought about by microbiological contaminants. There additionally remains a need to respond to the preference of the consuming public for such mayonnaise spreads that are not excessively tart due to low pH values. As a corollary, such high moisture mayonnaise spreads having low acid contents must remain resistant to growth by microorganisms that may contaminate them from the environment. This invention addresses these needs.